2020 Volume 58 Issue 1 Pages 4-13
Low cycle fatigue tests were conducted on industrial pure iron (electromagnetic soft iron) after hydrogen pre-charging. The effect of hydrogen on fatigue life was examined, in combination with stress response during monotonic and cyclic straining. The hydrogen desorption behavior was determined by thermal desorption analysis (TDA) on specimen interrupted at 10, 30 or 100 cycles with hydrogen post-charging. Comparing to the results without hydrogen pre-charging, the effect of hydrogen pre-charging was discussed. The hydrogen pre-charging degraded the fatigue life down to 1⁄8. Although the upper and lower yield strengths became lowered by hydrogen pre-charging, the stress range during cycling exceeded that of without hydrogen pre-charging. The amount of hydrogen that were trapped by either dislocation, grain boundary, vacancy or vacancy cluster tended to increase with strain cycling, with⁄without hydrogen pre-charging. Hydrogen pre-charging prompted the appearance of hydrogen that was trapped by vacancy and vacancy cluster. The hydrogen trapped by vacancy cluster was most of all affected by hydrogen pre-charging and strain cycling:It could be correlated with the fraction (N⁄Nf) , where N is number of interrupted cycles and Nf is that of fatigue life. The reduced yield strength with hydrogen pre-charging may be caused by substitution of carbon atoms by hydrogen atoms, which are interacting with dislocation. The increased stress range during cycling may be originated by hydrogen coupled with fresh born vacancy to suppress the mobility of dislocation.
